The invention relates to solid oxide fuel cell (SOFC) stacks and, more particularly, to a compliant seal for positioning between layers of components that form the stack.
The primary function of such seals is to prevent mixing of gaseous reactants used in an SOFC stack. In order for the seals to provide the desired function, it is necessary that the seals possess mechanical and chemical stability at high temperature and moist-reducing conditions present within an SOFC stack. In addition, the seals must maintain structural integrity under operation and thermal cycling conditions.
Conventional seals are made of glass or glass-based ceramics where the thermal expansion properties are tailored to match that of the cell and stack components such that the seals maintain structural integrity on thermal cycling. These glasses are typically made of oxides containing silicon, boron, or phosphorous and typically contain additions of alkali metal oxides. Unfortunately, these oxides tend to contaminate the cells and adversely affect the long-term performance of the cells and stack. In addition, these glasses are not chemically stable in moist-reducing environments and do not provide structural integrity for long-term applications.
Prior art seals for SOFC's also include the use of gaskets made of discontinuous ceramic fibers mixed with ceramic particles. Such seals leak and result in gas mixing, loss of efficiency and possible degradation of the cell performance.
Based upon the foregoing, it is clear that the need remains for an improved impermeable seal that does not contaminate or otherwise adversely affect cell performance and is chemically and mechanically stable under long-term operating and thermal cycling conditions.
It is therefore the primary object of the present invention to provide such a seal.
Other objects and advantages of the present invention will appear hereinbelow.